1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive for applying an optically functional film, an optically functional film with the pressure-sensitive adhesive and a production process for the same, and an optical film using the above optically functional film with the pressure-sensitive adhesive and a production process for the same. More specifically, the present invention relates to a pressure-sensitive adhesive for an optically functional film which is suitably laminated on a polarizing plate, particularly a polarizing plate integrated with a viewing angle expanding film or a retardation film or a polarizing plate comprising a retardation film laminated thereon and can apply the above polarizing plate on a liquid crystal cell or a retardation film with good durability and which has the characteristics that a liquid crystal display (LCD) obtained therefrom is less liable to cause light leakage even under the environment of high temperature and high humidity and that static electricity is less liable to be produced when peeling off a release film from a pressure-sensitive adhesive layer, an optically functional film with the above pressure-sensitive adhesive and a production process for the same, and an optical film and a production process for the same.
2. Description of the Related Art
A durability which does not bring about lifting and peeling even under various environments and a performance which can prevent light leakage in a liquid crystal cell are required to a pressure-sensitive adhesive used for applying a polarizing plate which is a member of a liquid crystal display with a liquid crystal cell. The above light leakage is caused as the result that a residual stress in a polarizing plate becomes uneven when a stress brought about by a change in a dimension such as shrinkage and expansion in the polarizing plate particularly under high temperature and high humidity environment can not be absorbed in a pressure-sensitive adhesive layer.
In order to solve the above problem on the light leakage, disclosed is a technique in which a pressure-sensitive adhesive is suitably softened and provided with a stress relaxation property by adding a low molecular weight substance such as a plasticizer to the pressure-sensitive adhesive (refer to, for example, a patent document 1). However, addition of the low molecular weight substance causes stain of the adherent when peeling off the polarizing plate and, in addition thereto, results in lowering the holding power, and lifting and peeling brought about by the passage of time are liable to be caused.
Accordingly, it is an issue to allow the adhesion durability and the light leakage preventing property to stand together.
On the other hand, in the case of a liquid crystal display which is operated by an IPS (in-plane-switching) system, a cell substrate on one side of a liquid crystal cell is subjected usually to ITO (indium tin oxide) treatment, but the opposite surface is not subjected to antistatic treatment. Accordingly, images are disturbed by static electricity generated in applying an optical film on a surface which is not subjected to ITO treatment. An optical film, a pressure-sensitive adhesive, a release film, a surface protecting film and the like are constituted by plastic materials and have a high electrical insulating property, and therefore they generate static electricity in rubbing and peeling. Accordingly, static electricity is generated when peeling off a release film and a surface protecting film from an optical film. Dirts and dusts in the periphery are introduced by the above static electricity, and when voltage is applied in the states that static electricity still remains, brought about are the problems that orientation of liquid crystal molecules is lost and that defect of a liquid crystal panel is caused.
Further, also in a finished liquid crystal panel, electrification is caused by bringing into contact with a diffusion film in an optical film at an incident side (lower surface) when wiping stains on the surface of the optical film at a visible side (upper surface) with a cloth and the like, and therefore the problem that the images are disturbed is involved therein. Also in a liquid crystal display which is operated by a VA (vertical alignment) system, the same problem is brought about in the case of a constitution in which a cell substrate subjected to ITO treatment is used only for one side of a liquid crystal cell.
In recent years, effective antistatic measures are strongly required as an increase in a size of a display equipment and an improvement in an driving system are advanced. Proposed is, for example, a method in which a surfactant having a low molecular weight is added to a pressure-sensitive adhesive to transfer the surfactant to the surface of the pressure-sensitive adhesive and in which moisture in the air is allowed to be adsorbed in the surfactant transferred to the surface of the pressure-sensitive adhesive to thereby exhibit the antistatic performance (refer to, for example, a patent document 2). However, it is difficult to satisfy both the antistatic performance and the pressure-sensitive adhesive property by the above method, and involved therein is the problem that the antistatic performance and an adhesive strength of the pressure-sensitive adhesive depend on temperature and humidity to a large extent.
Patent document 1: Japanese Patent No. 3272921
Patent document 2: Japanese Patent Application Laid-Open No. 138901/1986